LS boat conversion
 

In process of swapping an LS into a sterndrive boat. Got most of the preliminary stuff sorted, but still have one unresolved item. The boat has a Mercruiser Alpha One Gen 2 outdrive and had a carb 4.3L originally. That setup uses an interruptor switch on the shift linkage to cut power to the ignition coil while the gears engage from neutral to forward or reverse. How in the world can I replicate this on the multi coil ignition system? I don’t want to turn the engine/ECU/main power off, just blip the ignition signal to the coils. Assume I will have a pull out 5.3L with full factory harness. Any ideas?

You could maybe interrupt the power to the injectors with a good relay. Assuming your just looking for a blip that should do it without excessive drama.. Check a LS wiring diagram but I believe its 1 or 2 fused connections to the injectors that then get grounded by the ECU to trigger them. Other option is to get a tuner to set up something that would cut your idle air way down while the switch is closed, kinda like the trigger for the AC..

As motorhead said you could still cut the power. Even to the coils. All 8 coils either share a common hot or hot wire for each bank.

Yup. Each side is powered by a single fuse. No reason at all you couldn't place an interupter in there before those feeds but I think you could probably tune it to be tame enough to allow smooth shifting. Consult a reputable tuner and work with what they suggest is a good route to ensuring your end result performs as expected.